Amsteel Line Question

[Rick D]

So, I had a clamshell sail cover put on the boat (good decision). The jack lines go through a couple of SS rings and those in turn go to a higher ring and then to a block on the second spreader. 7mm Amsteel.
So, I was doing some work and had the cover pretty far open. When I finished, I tensioned it again but found a twist, maybe four turns, at the top. I couldn't figure it out since nothing had been disconnected. Anyhow, my wife and I untied the jacks and took the twist out and then I again retensioned them, with the same result. Finally, with the twist again all out, my wife told me that the twist occurred when I tensioned it.
So, I can only surmise the lay of the line causes a twist when it is in tension. Very odd. Any thoughts? Any experience? Quirky stuff.

 

[Jackdaw]

Weird indeed. Dyneema really doesn't have a 'lay'. How are you tightening it?

 

[Rick D]

Weird indeed. Dyneema really doesn't have a 'lay'. How are you tightening it?

Just by hand; enough tension to pull the cover up but not much. !0 pounds maybe. I wondered if the block might have something to do with it but I don't know why it would. What's weird is that I can remove the tension and let it down, which I would assume would let any twist unwind. But when I retension it, it comes back. Makes no sense to me. It must generate some real torque to put four twists in.

 

[Ron20324]

When you put the line on, did you unwind it off a rolling spool, or did you pull it off the side, creating a natural spiral in the line? might have to pull it back out and let it hang like a telephone cord to let the kinks out.

 

[Rick D]

When you put the line on, did you unwind it off a rolling spool, or did you pull it off the side, creating a natural spiral in the line? might have to pull it back out and let it hang like a telephone cord to let the kinks out.

Good question. It came pre-rigged, so it had plenty of time to settle. it's been up a while, but only two trips on it.

 

[Gunni]

Amsteel would not be my choice for sail bag jack lines. It has a tendency to lock and not rotate under load where it turns around a sharp turn. In any case a fine braided Dacron line has plenty of strength for this job and costs a lot less.

 

[CloudDiver]

Can you take some pictures of the rigging and where the twist occurs? I'm scratching my head on this one... Like @Jackdaw mentioned above, there is no 'lay' in Amsteel, most Dyneema lines are 12 strand single braid. I love the stuff for it's multitude of uses, just watch for chafe and UV degradation but you should get a minimum of 5 years and as much as 8 depending on the application and how much wear it gets. You could consider adding a sleeve to extend its life.

 

[CloudDiver]

Agree... 7mm Amsteel is big and strong enough to use as standing rigging (although a heat annealed Dyneema would be the better choice). For these jack lines polyester is fine, but if you insisted on Dyneema 3mm would be more than ample.

Amsteel would not be my choice for sail bag jack lines. It has a tendency to lock and not rotate under load where it turns around a sharp turn. In any case a fine braided Dacron line has plenty of strength for this job and costs a lot less.

 

[Rick D]

Thanks guys. 7mm Amsteel is what Quantum spec'd and shipped. Pretty slippery stuff and I assume that is why they chose it. It came pre-rigged from whatever central facility they use. (The local guy measures and gets delivery for installation.) The lazy jacks I had on it before were 3/16 Dacron and were going well at 22 years old. They were originally attached to a clamshell cover I HATED and got rid of after a year and converted to a straight lazy jack system. It was less frustrating but still not as useful as this Quantum unit that I'm pretty impressed with. I'll take a photo next time I go to the boat (next week sometime). Anyhow, it is an oddity. Like I said, it was clear from my wife's vantage point that as I increased the tension on the line, the same line induced twist at the connection ring. In other words just like a new three-strand might. Weird.

 

[Gunni]

Seriously, take amsteel 12 braid around a 90 degree fixed pin with load and observe the cross-section. It is flat and that inhibits line rotation. The stuff is great for straight shot loads but this is not one of those applications.

 

[Rick D]

Seriously, take amsteel 12 braid around a 90 degree fixed pin with load and observe the cross-section. It is flat and that inhibits line rotation. The stuff is great for straight shot loads but this is not one of those applications.

That is what I observed and concluded. Thus the puzzle. The block may be the issue but I don't know why.

 

[Gunni]

That is what I observed and concluded. Thus the puzzle. The block may be the issue but I don't know why.

The amsteel wraps the spreader block at something more like 135 degrees, under load the situation is the same - flat braid, no rotation. I would ask Quantum to switch the line out to Dacron cored braid and explain why the problem went away.

 

[Sanctuary2]

So, I had a clamshell sail cover put on the boat (good decision). The jack lines go through a couple of SS rings and those in turn go to a higher ring and then to a block on the second spreader. 7mm Amsteel.
So, I was doing some work and had the cover pretty far open. When I finished, I tensioned it again but found a twist, maybe four turns, at the top. I couldn't figure it out since nothing had been disconnected. Anyhow, my wife and I untied the jacks and took the twist out and then I again retensioned them, with the same result. Finally, with the twist again all out, my wife told me that the twist occurred when I tensioned it.
So, I can only surmise the lay of the line causes a twist when it is in tension. Very odd. Any thoughts? Any experience? Quirky stuff.

I've been watching a lot of videos about thimbles with dyneema and found this video (there are others) that address twist in the line:

Perhaps a solution? Just a thought.